Search found 76 matches

by Chris Walton
Sat Oct 05, 2013 6:42 pm
Forum: Language Issues
Topic: Expression evaluation
Replies: 4
Views: 8892

Re: Expression evaluation

Prior to your response, I was rechecking "Inheritance Model". My issue arises from section 10 of that document. For the first time using Rel/Tutorial D, I feel I disagree with a design point of the language, rather than merely failing to understand the syntax. As a consequence I will raise...
by Chris Walton
Sat Oct 05, 2013 3:07 pm
Forum: Language Issues
Topic: Expression evaluation
Replies: 4
Views: 8892

Re: Expression evaluation

So what if there are more than one subtype; with overlapping constraints such as (an addition to my previous example): TYPE positive_ub_integer IS { unbounded_integer CONSTRAINT ( CAST_AS_INTEGER ( THE_VALUE ( unbounded_integer ) ) > 0 ) OR THE_VALUE( unbounded_integer ) = "unbounded" POSS...
by Chris Walton
Fri Oct 04, 2013 6:16 pm
Forum: Language Issues
Topic: Expression evaluation
Replies: 4
Views: 8892

Expression evaluation

I am puzzled by the action of the type system in some respects and am seeking clarification. If you think this query would be better directed to Hugh Darwen, I will submit it on the TTM list. I have defined two types, one inheriting from the other, and one operator on the parent type as follows: TYP...
by Chris Walton
Tue Oct 01, 2013 12:10 pm
Forum: Language Issues
Topic: Relation valued parameters
Replies: 5
Views: 10633

Re: Relation valued parameters

Thanks for the pointer to an example - I'll pursue that.
by Chris Walton
Mon Sep 30, 2013 4:03 pm
Forum: Language Issues
Topic: Relation valued parameters
Replies: 5
Views: 10633

Re: Relation valued parameters

Could you possibly expand on your suggestion a little - would the syntax simply be execute.......(the listing of my statement)? I am finding that I am writing quite a lot of boilerplate code such as: VAR Dir VIEW WITH ( A := ( sys.Catalog WHERE Owner <> "Rel" ) { Name, Definition }, B := (...
by Chris Walton
Fri Sep 27, 2013 3:15 pm
Forum: Language Issues
Topic: Relation valued parameters
Replies: 5
Views: 10633

Relation valued parameters

Is it possible to define operators which have, as their parameters, relations of any type? Below is my naive attempt to define such an operator.

OPERATOR test ( P RELATION, Q RELATION ) RETURNS RELATION;
return P JOIN Q;
END OPERATOR ;
by Chris Walton
Tue Sep 03, 2013 3:53 pm
Forum: Rel Examples
Topic: Rationale for developing another type system.
Replies: 3
Views: 9705

Re: Rationale for developing another type system.

I have not read Databases, Types and the Relational Model. It is apparently out of print, and not likely to be reprinted. At least this is the information I received when I oredered it. I have read several of Date's and Darwen's books, and some notes and other papers that have been published. These ...
by Chris Walton
Tue Sep 03, 2013 3:40 pm
Forum: Language Issues
Topic: Expectations of a type system
Replies: 2
Views: 7258

Re: Expectations of a type system

I note what you say about composition - I have not yet explored that.I would certainly agree with you about the lack of distinction between UDTs and BDTs, except for one thing. In approaching the built in types in Rel in the way I did - unsure of the capabilities of Rel, and the implications in term...
by Chris Walton
Wed Aug 28, 2013 5:31 pm
Forum: Language Issues
Topic: Expectations of a type system
Replies: 2
Views: 7258

Expectations of a type system

The following is the note I put together when compiling Ex10 in the example forum. As I am having some difficulty in getting to grips with the type model in TTM/Tutorial D/Rel, I have listed some of the behaviour I expect from a type system. Some of this behaviour is present in Rel and some not. Thi...
by Chris Walton
Wed Aug 28, 2013 5:26 pm
Forum: Rel Examples
Topic: Rationale for developing another type system.
Replies: 3
Views: 9705

Rationale for developing another type system.

***NOTE*** This posting has been superseded by that dated 2013-11-13 below. This version has been retained, to keep the thread coherent. The new version replaces this one completely. ***NOTE*** This is the note I included in Ex 10, with my rationale for using a type system as the example, when Rel ...
by Chris Walton
Wed Aug 28, 2013 5:24 pm
Forum: Rel Examples
Topic: Ex 10 A type system
Replies: 3
Views: 12783

Ex10 Type definition system

EDITED 2013-11-17 incorporating substantial refinements of the system. // // Bootstrap // OPERATOR LENGTH(s CHAR) RETURNS INTEGER Java FOREIGN return ValueInteger.select(context.getGenerator(), s.stringValue().length()); END OPERATOR; TYPE ID POSSREP { VALUE CHARACTER CONSTRAINT LENGTH ( VALUE ) <= ...
by Chris Walton
Wed Aug 28, 2013 5:21 pm
Forum: Rel Examples
Topic: Ex 10 A type system
Replies: 3
Views: 12783

Re: Ex 10 A type system

OK - I'll put the script in this thread; the expectations in language discussions; and the rationale as a separate thread.
by Chris Walton
Tue Aug 27, 2013 2:34 pm
Forum: Language Issues
Topic: Simple supertype, complex subtype
Replies: 4
Views: 9535

Re: Simple supertype, complex subtype

Thanks - that does exactly what I am trying to do. It is amazing how obscure the simple solution can be.
by Chris Walton
Tue Aug 27, 2013 2:11 pm
Forum: Rel Examples
Topic: Ex 10 A type system
Replies: 3
Views: 12783

Ex 10 A type system

Ex 10 A type system This example is a reasonable sized system to illustrate many aspects of the syntax, particularly as it relates to data types and operators. The attached archive contains the following three files: script.txt - to generate the complete type system Why.txt - a full description of w...
by Chris Walton
Mon Aug 26, 2013 9:55 am
Forum: Language Issues
Topic: Simple supertype, complex subtype
Replies: 4
Views: 9535

Re: Simple supertype, complex subtype

I am trying to define data types within a type system. The data type supertype is called base_data_type. This has a number of subtypes, such as arbitrary, symbolic, etc. One of these subtypes is time related - test_date below. This subtype can be represented as YYMM. So the components of test_date a...